Method of Dyeing or Printing Cellulosic Fibre Materials With Vattable Dyes

ABSTRACT

A method of dyeing or printing cellulosic fibre materials wherein the fibre material is brought into contact with at least one vattable dye and at least one quinoid compound in an aqueous composition at a pH of less than 12 (electrochemical methods being excluded) yields level and tinctorially strong dyeings.

The present invention relates to a method of dyeing or printing cellulosic fibre materials with vattable dyes, which in the context of this invention are to be understood as including both vat dyes and sulfur dyes.

The dyeing or printing of cellulosic textile materials with vat dyes is generally known. In order to impart the required substantivity to the water-insoluble vat dye, that is to say in order to fix it on the textile material, it must first be converted into a substantive water-soluble leuco form by reduction (vatting) and then developed to the dye pigment again by oxidation.

In the dyeing of denim, normally the only dye used is indigo and the only fibre used is 100% cotton. In a single-pass dyeing operation, only about 10 to 20% of leuco indigo is absorbed by the fibres. Because of this low bath exhaustion, dyeing with indigo by batchwise exhaust processes is not very widespread. It is therefore usual to carry out the dyeing process continuously in several passes, i.e. in several steps. Very long machines having from 8 to 10 units are accordingly used, each unit consisting of an application device for the vat (padding machine) and a subsequent skying stage for re-oxidation. In such a method, which usually allows yarn to be dyed in the form of a rope or hank or in the form of a warp sheet, the vatted indigo dye is applied from a plurality of dye liquors of large volume by repeated brief immersion as well as squeezing out and oxidation in the intermediate skying stages.

The vat is at room temperature in all cases, and so the padding machine is not heatable. In this way there is obtained an indigo dyeing in which virtually only the outer fibres of the yarns are coloured by the dye and those fibres are themselves dyed only very superficially (ring dyeing). By abrasion in stone-wash treatments, the dye is rubbed away especially on exposed areas of the made-up denim article. As a result, the readily visible ageing process desired by the market is obtained, that process also continuing during domestic washing.

Two types of machine are usually used for dyeing warp yarn for denim: the hank or rope dyeing machine, in which the warp yarns are brought together to form a plurality of hanks or ropes (rope dyeing), or the open-width dyeing machine, in which the warp yarn is dyed in open width (slasher dyeing). A sizing process is integrated into the dyeing process. Thereafter, the dyed yarn is woven with an undyed, raw weft yarn.

The colour yield of indigo in the region of about pH 11.5 is substantially higher than at pH 12.5 to 13. In addition, the diffusion of indigo into the fibres is greater in the higher pH range, which reduces the surface effect desired for denim. It is therefore advantageous to carry out dyeing with indigo in a range around pH 11.5 in order to obtain a good colour yield with the desired ring-dyeing effect. In industrial indigo dyeing machines, however, not all dye baths have an alkali metering unit with pH monitoring, so that monitoring the pH is a problem.

In addition to traditional blue denim there is a demand for denim goods that include other colour shades and likewise exhibit the desired “stone-wash” effect. Unlike indigo, however, most vat dyes are in their leuco form distinguished by a higher affinity for the fibres and accordingly by higher bath exhaustion, making it virtually impossible for ring-dyed yarn to be produced under the conditions of indigo dyeing. Such vat dyes therefore cannot be applied under the conventional conditions of indigo dyeing.

The problem underlying the present invention is to provide an economical method of dyeing and printing cotton in indigo and non-indigoid shades, which method can be carried out especially under the conditions of indigo dyeing on conventional types of machine and enables a broad spectrum of colours to be obtained. The dyeings should also exhibit a high degree of levelness, high tinctorial strength and depth of shade as well as the ring-dyeing effect which is characteristic of classic denim articles.

The present invention accordingly relates to a method of dyeing or printing cellulosic fibre materials, wherein the fibre material is brought into contact with at least one vattable dye and at least one quinoid compound in an aqueous composition at a pH of less than 12, electrochemical methods being excluded.

In the method according to the invention, the cellulosic fibre material is dyed or printed with vattable dyes, such as e.g. vat dyes or sulfur dyes, preferably vat dyes. The vat dyes are either indigo or anthraquinoid or indigoid dyes. Vat dyes and sulfur dyes have been known for a long time, are commercially available and are described e.g. in the Colour Index (C.I.), 3rd Edition, 1971, Volume 3, pages 3719 to 3844 and also in Volume 4 under C.I. Nos. 58000 to 74000.

Vat dyes suitable for the method according to the invention correspond e.g. to formulae

Quinoid compounds are e.g. derivatives of benzoquinone, naphthoquinone, acenaphthenequinone or anthraquinone containing halogen, amino, hydroxy, carboxylic acid and/or sulfonic acid groups, such as hydroxyanthraquinones, e.g. 2-hydroxyanthraquinone, 1,2-dihydroxyanthraquinone or 1,4-dihydroxyanthraquinone, haloanthraquinones, e.g. 1-chloro-anthraquinone, anthraquinonecarboxylic acids, anthraquinonesulfonic acids, e.g. anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid, anthraquinone-1,5-disulfonic acid, anthraquinone-2,6-disulfonic acid or 1,4-diaminoanthraquinone-2-sulfonic acid. The said quinoid compounds can be used singly or in admixture.

Preferred as quinoid compounds are anthraquinones, preferably anthraquinones containing sulfonic acid groups, such as e.g. anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid, anthraquinone-1,5-disulfonic acid or anthraquinone-2,6-disulfonic acid and especially anthraquinone-2-sulfonic acid.

The acid-group-containing quinoid compounds are either in free acid form or, preferably, in salt form. Salts that come into consideration include, for example, the alkali metal, alkaline earth metal and ammonium salts or the salts of an organic amine. Examples that may be mentioned include the sodium, lithium, potassium and ammonium salts and mono-, di- and tri-ethanolamine salts.

The method according to the invention is carried out e.g. at a pH of from 11.2 to 11.8, preferably from 11.3 to 11.6.

The pH can be adjusted by using e.g. sodium carbonate or an alkali metal hydroxide customarily used in indigo dyeing, such as e.g. sodium hydroxide. Sodium carbonate can either be used alone or in combination with alkali metal hydroxide. With a view to improved colour yield it is advantageous to stabilise the pH in the dyebaths, for example when there is used instead of the indigo usually employed a combination of e.g. two or three dyes, the colour yield of which depends on the pH in different ways.

In the method according to the invention, sodium carbonate is used e.g. in an amount of from 10 to 20 μl, preferably from 12 to 18 μl and especially 16 g/l, based on the dye liquor.

The amount of vattable dyes in the liquor is governed by the desired tinctorial strength. In general, amounts of from 0.001 to 25% by weight, especially from 0.01 to 20% by weight, based on the weight of the cellulosic fibre material used, have proved suitable.

In order to dye the fibre materials with the vattable dyes it is necessary first to convert the dyes into the water-soluble leuco form. The reducing agents customary for vat dyeing are therefore added to the dye liquors in addition to the vattable dye and the alkali, there coming into consideration especially hydrosulfite (dithionite), such as e.g. sodium hydrosulfite (sodium dithionite).

The reducing agents are used, for example, in an amount of at least 100% by weight, based on the amount of vattable dye.

The quinoid compounds are used e.g. in an amount of from 5 to 100% by weight, preferably from 25 to 75% by weight, based on the amount of vattable dye.

In addition, the dye liquor may comprise further dyeing auxiliaries, e.g. electrolytes such as sodium chloride or sodium sulfate or commercially available wetting agents, levelling agents and dispersants.

In accordance with the method of the invention, preference is given to dyeing cellulosic fibre materials in an aqueous liquor, wherein the vat dye mixture can be applied from an aqueous solution by the pad-dyeing or exhaust methods conventional in vat dyeing. The liquor ratio is dependent upon the equipment parameters, upon the substrate and upon the make-up. It can vary within wide ranges, e.g. from 1:4 to 1:100, preferably from 1:6 to 1:20. The pad-dyeing method is preferred.

The dyeing method can be carried out at temperatures of e.g. from 20 to 110° C., especially from 20 to 80° C. The method according to the invention is preferably carried out at about 20° C., i.e. room temperature, in which case a heating device for heating the dye liquor is not required.

The dyeing process is advantageously carried out continuously in a plurality of passes. A plurality of passes means at least two, three, four, five or six passes, preferably at least four, five or six passes. As an upper limit, eight, nine or ten passes, for example, are carried out. Preference is given to dyeing in from four to ten passes, especially from six to eight passes.

The dyeing process according to the invention can advantageously be carried out using conventional types of machine, for example a hank dyeing machine or an open-width dyeing machine, which are widely used in industrial indigo dyeing.

As cellulosic fibre materials there come into consideration especially non-pretreated cellulose, such as e.g. hemp, linen, natural cotton, as well as fibre blends, e.g. polyacrylic/cotton or polyester/cotton blends. Fibre materials based on regenerated cellulose (viscose) are also suitable. The cellulose material may be in a wide variety of processing forms, e.g. in the form of yarn, woven material, nonwoven material or knitted fabrics.

By means of the method according to the invention, cellulosic fibre material, e.g. yarn in the form of a hank or rope or in the form of a warp sheet, can be dyed in indigoid or non-indigoid shades in an advantageous and reliable manner.

The dyeings obtained using the method according the invention are distinguished by good levelness and also exhibit good colour yields, good fastness to light and good fastness to wetting. By means of the method according to the invention it is possible to produce strongly ring-dyed warp yarn which, after appropriate treatment, exhibits the desired “stone-wash” effect.

The Examples which follow serve to illustrate the invention. Temperatures are given in degrees Celsius, parts are parts by weight and percentages refer to % by weight, unless otherwise indicated. Parts by weight relate to parts by volume in a ratio of kilograms to litres.

EXAMPLE 1

100 ml of a dye liquor (vat) are prepared by dispersing in water 13.3 g/l of a dye formulation containing 30% by weight finely ground pigment of formula (4) and 10% by weight dispersant. 2 g/l of anthraquinone-2-sulfonic acid in sodium salt form, 16 g/l of calcined soda and 4 g/l of sodium hydrosulfite (sodium dithionite) are then dissolved in the resulting mixture.

2 g of warp yarn of 100% bleached cotton are immersed for 20 seconds in the dye liquor, which is maintained at room temperature. The warp yarn piece is then squeezed out on a padding machine to a liquor pick-up of 70% and, for re-oxidation of the dye, developed in air for 80 seconds.

The steps of immersion, squeezing out and skying are carried out a total of eight times with the same warp yarn piece and the same dye liquor, during which the pH of the dye liquor is maintained at from 11.5 to 11.6 by periodic addition of 10% sodium hydroxide solution. The dyeing is then subjected to cold and hot rinsing and subsequently dried.

A level, olive-grey cotton dyeing of high tinctorial strength is obtained which has the typical ring-like dye distribution in the fibre cross-section, the dyes being located only at the surface of the fibres (visible by means of a microscope). The dyeing produces the wear pattern typical in “stone-wash” treatments, like that in commercial, conventional denim goods.

COMPARISON EXAMPLE 1

When a procedure as described in Example 1 is carried out, but the addition of anthraquinone-2-sulfonic acid in sodium salt form is omitted, the dyed warp yarn exhibits a significantly reduced depth of shade.

EXAMPLE 2

100 ml of a dye liquor (vat) are prepared by dispersing in water 26.7 g/l of a dye formulation containing 30% by weight finely ground pigment of formula (4) and 10% by weight dispersant. 4 g/l of anthraquinone-2-sulfonic acid in sodium salt form, 16 g/l of calcined soda and 15 μl of sodium hydrosulfite (sodium dithionite) are then dissolved in the resulting mixture.

2 g of warp yarn of 100% bleached cotton are immersed for 20 seconds in the dye liquor, which is maintained at room temperature. The warp yarn piece is then squeezed out on a padding machine to a liquor pick-up of 70% and, for re-oxidation of the dye, developed in air for 80 seconds.

The steps of immersion, squeezing out and skying are carried out a total of eight times with the same warp yarn piece and the same dye liquor, during which the pH of the dye liquor is maintained at from 11.5 to 11.6 by periodic addition of 10% sodium hydroxide solution. The dyeing is then subjected to cold and hot rinsing and subsequently dried.

A level, olive-grey cotton dyeing of high tinctorial strength is obtained which has the typical ring-like dye distribution in the fibre cross-section, the dyes being located only at the surface of the fibres (visible by means of a microscope). The dyeing produces the wear pattern typical in “stone-wash” treatments, like that in commercial, conventional denim goods.

COMPARISON EXAMPLE 2

When a procedure as described in Example 2 is carried out, but the addition of anthraquinone-2-sulfonic acid in sodium salt form is omitted, the dyed warp yarn exhibits a significantly reduced depth of shade.

EXAMPLE 3

100 ml of a dye liquor (vat) are prepared by dispersing in water 20.0 g/l of a dye formulation containing 20% by weight finely ground pigment of formula (3) and 10% by weight dispersant. 2 g/l of anthraquinone-2-sulfonic acid in sodium salt form, 16 g/l of calcined soda and 10 g/l of sodium hydrosulfite (sodium dithionite) are then dissolved in the resulting mixture.

2 g of warp yarn of 100% bleached cotton are immersed for 20 seconds in the dye liquor, which is maintained at room temperature. The warp yarn piece is then squeezed out on a padding machine to a liquor pick-up of 70% and, for re-oxidation of the dye, developed in air for 80 seconds.

The steps of immersion, squeezing out and skying are carried out a total of eight times with the same warp yarn piece and the same dye liquor, during which the pH of the dye liquor is maintained at from 11.5 to 11.6 by periodic addition of 10% sodium hydroxide solution. The dyeing is then subjected to cold and hot rinsing and subsequently dried.

A level, red cotton dyeing of high tinctorial strength is obtained which has the typical ring-like dye distribution in the fibre cross-section, the dyes being located only at the surface of the fibres (visible by means of a microscope). The dyeing produces the wear pattern typical in “stone-wash” treatments, like that in commercial, conventional denim goods.

COMPARISON EXAMPLE 3

When a procedure as described in Example 2 is carried out, but the addition of anthraquinone-2-sulfonic acid in sodium salt form is omitted, the dyed warp yarn exhibits a significantly reduced depth of shade. 

1. A method of dyeing or printing cellulosic fibre materials, wherein the fibre material is brought into contact with at least one vattable dye and at least one quinoid compound in an aqueous composition at a pH of less than 12, electrochemical methods being excluded.
 2. A method according to claim 1, wherein an anthraquinone containing sulfonic acid groups is used as quinoid compound.
 3. A method according to claim 1, wherein anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid, anthraquinone-1,5-disulfonic acid or anthraquinone-2,6-disulfonic acid is used as quinoid compound.
 4. A method according to claim 1, wherein cellulosic fibre materials are dyed in an aqueous liquor.
 5. A method according to claim 4, wherein the pH is from 11.2 to 11.8.
 6. A method according to claim 5, wherein sodium carbonate is used as alkali.
 7. A method according to claim 6, wherein sodium carbonate is used in an amount of from 10 to 20 g/l, based on the liquor.
 8. A method according to claim 1, wherein the dye is applied by the pad-dyeing method.
 9. A method according to claim 1, wherein the dyeing process is carried out continuously in a plurality of passes.
 10. A method according to claim 1, wherein the dyeing process is carried out on a hank dyeing machine or an open-width dyeing machine. 